1. Field of the Invention
The present invention generally relates to a hydraulic blow molding of a container from a preform, wherein the end product, a liquid, is used as the blow molding medium. More specifically, the present invention relates to preventing distortion and/or deformation of the finish of a preform during the hydraulic blow molding process.
2. Description of Related Art
Plastic containers for liquids are manufactured by various different methods. In most methods, a plastic preform is heated to a suitable temperature for molding, placed within a mold and then expanded axially in radially to form the container. In certain processes, air is used as a blow molding medium to expand the preform. In other processes, the liquid product is used as the blow molding medium. This latter process, using the liquid end product as the blow molding medium, is herein referred to as hydraulic blow mold.
With hydraulic blow molding, the blow molding medium is injected under pressure and generally, in a non-hot fill process, at a temperature in the range of about 0° C. to 32° C. (32° F. to 90° F.) and, in a hot fill process, at a temperature of between about 85° C. and 95° C. (about 185° F. to 195° F.). In many instances, as seen from these temperature ranges, the temperature of the blow molding medium is greater than ambient.
While the body of the preform is axially elongated in radially expanded during the hydraulic blow molding process, the neck or finish of the preform is intended to remain in its initially formed shape. It is important that the finish remain in its initially formed shape since the finish includes threads and sealing surfaces that must be engaged by a closure. It is possible that during hydraulic blow molding, particularly when the blow molding medium as an elevated temperature relative to the temperature of the preform, that the finish will distort and/or deformed as a result of either exposure to the temperature of the blow molding medium or its injection pressure. This becomes more likely when the wall thickness of the finish is reduced in an effort to make the resultant container more light weight.
In order to protect the finish, various strategies have been proposed. US 2013/0164404 discloses a system in which a counter pressure is applied to the exterior of the finish during the blow molding process. WO 2013/145511 similarly discloses a system in which a counter pressure is applied to the exterior of the finish during the blow molding process.
In view of the above, it is apparent that there exists a need for a system in which the finish of a preform is protected during the hydraulic blow molding process, not only from pressure interior of the preform during the process, but also from temperatures of the blow molding medium that result in the finish being susceptible to deformation and distortion.